void setup() {
  size(600,600);
  background(220);
  smooth();
  noStroke();
}  
void draw() {
  float ang = map(millis()%60000,0,60000,-HALF_PI,3*HALF_PI);
  if (ang==0) {
    background(220);
  } 
  arc(width/2, height/2, width, height,-HALF_PI, ang);   
}


